Input: exc3000 - add support to query model and fw_version

Expose model and fw_version via sysfs. Also query the model
in probe to make sure, that the I2C communication with the
device works before successfully probing the driver.

This is a bit complicated, since EETI devices do not have
a sync interface. Sending the commands and directly reading
does not work. Sending the command and waiting for some time
is also not an option, since there might be touch events in
the mean time.

Last but not least we do not cache the results, since this
interface can be used to check the I2C communication is still
working as expected.

Reviewed-by: Enric Balletbo i Serra <[e-mail]>
Signed-off-by: Sebastian Reichel <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Dmitry Torokhov <[e-mail]>

Documentation/ABI/testing/sysfs-driver-input-exc3000

···
+What:		/sys/bus/i2c/devices/xxx/fw_version
+Date:		Aug 2020
+Contact:	[e-mail]
+Description:    Reports the firmware version provided by the touchscreen, for example "00_T6" on a EXC80H60
+
+		Access: Read
+		Valid values: Represented as string
+
+What:		/sys/bus/i2c/devices/xxx/model
+Date:		Aug 2020
+Contact:	[e-mail]
+Description:    Reports the model identification provided by the touchscreen, for example "Orion_1320" on a EXC80H60
+
+		Access: Read
+		Valid values: Represented as string

drivers/input/touchscreen/exc3000.c

···
 #define EXC3000_LEN_FRAME		66
 #define EXC3000_LEN_POINT		10
 
+#define EXC3000_LEN_MODEL_NAME		16
+#define EXC3000_LEN_FW_VERSION		16
+
 #define EXC3000_MT1_EVENT		0x06
 #define EXC3000_MT2_EVENT		0x18
 
···
 	struct gpio_desc *reset;
 	struct timer_list timer;
 	u8 buf[2 * EXC3000_LEN_FRAME];
+	struct completion wait_event;
+	struct mutex query_lock;
+	int query_result;
+	char model[EXC3000_LEN_MODEL_NAME];
+	char fw_version[EXC3000_LEN_FW_VERSION];
 };
 
 static void exc3000_report_slots(struct input_dev *input,
···
 	return 0;
 }
 
+static int exc3000_query_interrupt(struct exc3000_data *data)
+{
+	u8 *buf = data->buf;
+	int error;
+
+	error = i2c_master_recv(data->client, buf, EXC3000_LEN_FRAME);
+	if (error < 0)
+		return error;
+
+	if (buf[0] != 'B')
+		return -EPROTO;
+
+	if (buf[4] == 'E')
+		strlcpy(data->model, buf + 5, sizeof(data->model));
+	else if (buf[4] == 'D')
+		strlcpy(data->fw_version, buf + 5, sizeof(data->fw_version));
+	else
+		return -EPROTO;
+
+	return 0;
+}
+
 static irqreturn_t exc3000_interrupt(int irq, void *dev_id)
 {
 	struct exc3000_data *data = dev_id;
···
 	u8 *buf = data->buf;
 	int slots, total_slots;
 	int error;
+
+	if (mutex_is_locked(&data->query_lock)) {
+		data->query_result = exc3000_query_interrupt(data);
+		complete(&data->wait_event);
+		goto out;
+	}
 
 	error = exc3000_read_data(data, buf, &total_slots);
 	if (error) {
···
 	return IRQ_HANDLED;
 }
 
+static ssize_t fw_version_show(struct device *dev,
+			       struct device_attribute *attr, char *buf)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	struct exc3000_data *data = i2c_get_clientdata(client);
+	static const u8 request[68] = {
+		0x67, 0x00, 0x42, 0x00, 0x03, 0x01, 'D', 0x00
+	};
+	int error;
+
+	mutex_lock(&data->query_lock);
+
+	data->query_result = -ETIMEDOUT;
+	reinit_completion(&data->wait_event);
+
+	error = i2c_master_send(client, request, sizeof(request));
+	if (error < 0) {
+		mutex_unlock(&data->query_lock);
+		return error;
+	}
+
+	wait_for_completion_interruptible_timeout(&data->wait_event, 1 * HZ);
+	mutex_unlock(&data->query_lock);
+
+	if (data->query_result < 0)
+		return data->query_result;
+
+	return sprintf(buf, "%s\n", data->fw_version);
+}
+static DEVICE_ATTR_RO(fw_version);
+
+static ssize_t exc3000_get_model(struct exc3000_data *data)
+{
+	static const u8 request[68] = {
+		0x67, 0x00, 0x42, 0x00, 0x03, 0x01, 'E', 0x00
+	};
+	struct i2c_client *client = data->client;
+	int error;
+
+	mutex_lock(&data->query_lock);
+	data->query_result = -ETIMEDOUT;
+	reinit_completion(&data->wait_event);
+
+	error = i2c_master_send(client, request, sizeof(request));
+	if (error < 0) {
+		mutex_unlock(&data->query_lock);
+		return error;
+	}
+
+	wait_for_completion_interruptible_timeout(&data->wait_event, 1 * HZ);
+	mutex_unlock(&data->query_lock);
+
+	return data->query_result;
+}
+
+static ssize_t model_show(struct device *dev,
+			  struct device_attribute *attr, char *buf)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	struct exc3000_data *data = i2c_get_clientdata(client);
+	int error;
+
+	error = exc3000_get_model(data);
+	if (error < 0)
+		return error;
+
+	return sprintf(buf, "%s\n", data->model);
+}
+static DEVICE_ATTR_RO(model);
+
+static struct attribute *sysfs_attrs[] = {
+	&dev_attr_fw_version.attr,
+	&dev_attr_model.attr,
+	NULL
+};
+
+static struct attribute_group exc3000_attribute_group = {
+	.attrs = sysfs_attrs
+};
+
 static int exc3000_probe(struct i2c_client *client)
 {
 	struct exc3000_data *data;
 	struct input_dev *input;
-	int error, max_xy;
+	int error, max_xy, retry;
 
 	data = devm_kzalloc(&client->dev, sizeof(*data), GFP_KERNEL);
 	if (!data)
···
 		data->info = &exc3000_info[eeti_dev_id];
 	}
 	timer_setup(&data->timer, exc3000_timer, 0);
+	init_completion(&data->wait_event);
+	mutex_init(&data->query_lock);
 
 	data->reset = devm_gpiod_get_optional(&client->dev, "reset",
 					      GPIOD_OUT_HIGH);
···
 		return -ENOMEM;
 
 	data->input = input;
+	input_set_drvdata(input, data);
 
 	input->name = data->info->name;
 	input->id.bustype = BUS_I2C;
···
 	error = devm_request_threaded_irq(&client->dev, client->irq,
 					  NULL, exc3000_interrupt, IRQF_ONESHOT,
 					  client->name, data);
+	if (error)
+		return error;
+
+	/*
+	 * I²C does not have built-in recovery, so retry on failure. This
+	 * ensures, that the device probe will not fail for temporary issues
+	 * on the bus.  This is not needed for the sysfs calls (userspace
+	 * will receive the error code and can start another query) and
+	 * cannot be done for touch events (but that only means loosing one
+	 * or two touch events anyways).
+	 */
+	for (retry = 0; retry < 3; retry++) {
+		error = exc3000_get_model(data);
+		if (!error)
+			break;
+		dev_warn(&client->dev, "Retry %d get EETI EXC3000 model: %d\n",
+			 retry + 1, error);
+	}
+
+	if (error)
+		return error;
+
+	dev_dbg(&client->dev, "TS Model: %s", data->model);
+
+	i2c_set_clientdata(client, data);
+
+	error = devm_device_add_group(&client->dev, &exc3000_attribute_group);
 	if (error)
 		return error;